Patch 5.4, Siege of Orgrimmar is currently slated to go live tomorrow and Wednesday, 10 and 11 September 2013.

As always, we here at WoWInterface will have our AddOn Survival Guide up and running to help you find when and where your favourite addons are updated for 5.4. Authors please note that we’ve got the 5.4 compatible tag enabled now.

From Blizzard’s patch notes for 5.4:

Of immediate interest for our community are the UI changes:

The vestigial Use Hardware sound option has been removed.

Authors, you can also check out this thread created by the community to document 5.4 API changes.